The present invention relates generally to heat pipes. More specifically, the present invention relates to a heat pipe which can be secured to a device by securing means and to which heat sink means can be selectively added to accurately control the amount of heat transferred.
A conventional heat pipe is a miniaturized, hermeticallly sealed evaporating and condensing system which functions to effect an axial transfer of thermal energy. The conventional heat pipe includes a sealed elongated container, preferably made of a heat conductive metal such as copper or aluminum, a capillary wick structure which is circumferentially secured to the interior surface of the container, and a quantity of working fluid such as mercury sufficient to at least partially saturate the wick structure. After the working fluid has been added to the system, the container is sealed while under a vacuum.
Since the container is sealed under a vacuum, the working fluid is in equilibrium with its own vapor. Thus, any application of heat to any external surface of the pipe will cause an instantaneous evaporation of working fluid near the heated surface. Heat transfer via heat pipe is highly efficient since the quantity of heat absorbed in the vaporization of a fluid is enormous compared to that absorbed during an increase of temperature of a liquid.
The vapor generated as a result of a heat addition creates a pressure gradient within the heat pipe which forces the vapor to an area of the heat pipe having a lower pressure and temperature. The lower temperature causes condensation of the vapor, thereby allowing the latent heat of vaporization to be dissipated into the condenser surfaces of the heat pipe. Heat may be removed from the condenser surfaces by conduction, convection or radiation into the surrounding environment.
After condensation, the condensed working fluid is returned to the evaporator region (i.e., where heat is added) by capillary pumping forces within the circumferential interior wick structure. This return may occur either with or without the aid of gravity.
Such conventional heat pipes have been used to transfer heat in many different applications. For example, one known heat pipe, which has a finned heat sink joined to a condenser end, is used to transfer heat from an internal combustion engine. Another known heat pipe is used to transfer heat from a modular, removable electrical heat-producing unit into a liquid containing storage chamber. It would be useful, however, to provide a heat pipe of which a portion could be selectively secured to a device by securing means and to which heat pipe a selected number of heat transferring surfaces could be selectively secured to accurately control the heat transfer process. Such a heat pipe could be used, for example, to transfer heat to selected parts of a conventional roto-mold to cause such parts to increase in temperature at the same rate as the general mold or even at a higher rate.
In general, rotational molding or roto-molding, is a method of making hollow plastic parts such as vehicle bumpers, toys, car head rests, water tanks, etc. In roto-molding, the parts are formed from a fine thermoplastic polymer powder (or liquid in some instances) within a closed metal mold which is first rotated in a heating chamber to melt the powder and then in a cooling chamber to solidify the part. Because of the rotation, the plastic powder covers all the interior surfaces of the mold. While the mold is rotating, it is placed inside a hot air oven so that as the mold heats up the plastic powder begins to stick to the inside of the mold and melts to form the desired shape. When the melted plastic has completely coated the mold inside surface, it is moved out of the oven and cooled by a medium such as air or water. After the mold has been cooled, it can be opened and the part removed.
The thickness of the plastic part produced in the roto-mold depends upon how fast each part of the mold surface heats up. If any mold surface heats up more slowly than the rest of the mold, that surface receives less plastic build-up and therefore a thinner plastic wall which makes for undesirable strength variations in the plastic part. It would therefore be desirable to provide a method and a means for transferring additional heat to selected parts of such a roto-mold and of accurately controlling the rate of such transfer.
It would also be useful to provide a means for withdrawing heat from selected portions of a device such as, for example, an electronic component structure. Such means could comprise a heat pipe a portion of which should preferably be easily securable to a hot portion of an electronic device to cool the electronic device. Easy securing of the heat pipe to the electronic device prevents the need for close tolerances or the necessity for having custom designed heat pipes for each specific electronic unit.
Accordingly, a means for accurately controlling the transfer of heat according to the present invention includes a heat pipe having a condenser end and an evaporator end with one of the ends being removably securable by securing means to a desired section of the device meant to be heated or cooled. A heat sink means, which is selectively positionable on the heat pipe and securable thereon by mounting means is also provided to enable additional heat to be transferred by the heat pipe.